65hp evinrude no power

[Capt dave 258]

I have a 1973, 65hp Evinrude that I need help with. The motor overheated to the point that it stalled. Since then I have changed the impeller, head and head gasket, exhaust manifold and gaskets, plugs and all 3 coils. I had it on the water today for the 1st time since overheating and it had limited power. I have compression in all 3 cylinders ranging from 150 to 155. When running, if I pull the top plug wire the motor runs noticeably worse and wants to stall. If I remove just the middle plug wire the engine stalls. When removing only the bottom plug wire, it has no noticeable difference, the motor still runs the same. When I go to reattach the bottom plug wire with the motor still running, I can hear the spark jumping from the wire lead to the plug. How can the 3rd cylinder run the same with or without the plug wire attached when it is clearly getting spark and has great compression? I read somewhere that it could be an exhaust issue? Any thoughts or ideas would be greatly appreciated.

 

[CaptnKingfisher]

I have a 1973, 65hp Evinrude that I need help with. The motor overheated to the point that it stalled. Since then I have changed the impeller, head and head gasket, exhaust manifold and gaskets, plugs and all 3 coils. I had it on the water today for the 1st time since overheating and it had limited power. I have compression in all 3 cylinders ranging from 150 to 155. When running, if I pull the top plug wire the motor runs noticeably worse and wants to stall. If I remove just the middle plug wire the engine stalls. When removing only the bottom plug wire, it has no noticeable difference, the motor still runs the same. When I go to reattach the bottom plug wire with the motor still running, I can hear the spark jumping from the wire lead to the plug. How can the 3rd cylinder run the same with or without the plug wire attached when it is clearly getting spark and has great compression? I read somewhere that it could be an exhaust issue? Any thoughts or ideas would be greatly appreciated.

I'm going to be lurking this post. Early in my wrenching I had the exact same problem on a V4 johnson. getting spark (7/16") to all cylinders good compression (120s) all cylinders yet cylinder drop test revealed I was running on two. Hope someone can help ya. I would say for the sake of being thorough, use an adjustable spark tester to measure your spark strength in that cylinder. Hearing the spark arcing to the block tells you you've got spark, but you could have weak spark. Worth being sure before moving on to other things diagnostically

 

[racerone]

That motor needs 4 things to run.-----Spark at the right time.-----Correct ( not too little and not too much ) amount of fuel.-----Compression in the crankcase.----Compression in the cylinder.-------So inspect your fuel pump diaphragm.----Costs no money.----For me it is hard to believe those compression numbers after a serious overheat that brought the motor to a " dynamic halt " as you say.----Should be easy to figure out what is wrong !

 

[Capt dave 258]

Borrowed a second compression tester and the results are as follows, 150, 150 and 140 in the cylinder that is "bad". Those readings are well within the 15% margin. Checked the fuel pump diaphram and it was fine. I'm wondering, since there are 3 carbs on that motor, could the carb that feeds that bottom, "bad" cylinder be plugged and not giving it gas? That would explain why it is getting spark but seems to be running only on the other two cylinders. Any reasonable way to test that carb to see if it's the issue??? Thanks!

 

[Capt dave 258]

Update. Was able to remove the drain screw from each of the carb bowls without removing the carbs. While removing the screw from each of the top carbs, gas drained out of the bowl. When removing the screw from the bottom carb, no gas came out. Removed gas supply hose to that carb with motor running and it's getting plenty of gas. Guessing that carb is plugged up somewhere. Going to have to remove the carbs and look into it. Not a fan of tinkering with carbs; not very good at it.

 

[F_R]

Delete

 

[racerone]

Those carburetors are very simple.----Be an easy fix.----But no fuel in one carburetor means that motor was running with no fuel going into that cylinder and no oil.----Fix the carburetor now.

 

[Capt dave 258]

Thank you for the input. Took the bottom carb off and apart. Float and needle seat looked good; no obvious blockage. Cleaned everything out as best I could and put it back on the boat. Started it up and no obvious change; pulled the spark plug wire for that cylinder and it ran the same with the wire on or off. Pulled the drain screw for the bowl on that carb and this time gas came out, so I know that gas is it at least in that carb. Switched coils and plugs around and still the same problem. Still no idea as to why that 3rd cylinder, which has good compression and spark is not firing properly.

 

[F_R]

So I'll rewrite what I started but deleted after you said the carb was dry.

Those motors simply cannot tolerate even a trace of overheating. It will warp the exhaust manifold baffle plate and it will squirt water into the cylinders. BUT you said you replaced those parts. Nevertheless make sure water isn't getting into the cylinders.

If it is leaking or not, I think you fried the pistons with that overheat to the point of seizure

 

[RBoyd1971]

Just curious, is the paint scorched on the head? Even if the piston is fried, 140 psi is good. It should run fine. For peace of mind, I would have to pull the head and see what they look like.

 

[Capt dave 258]

How can the pistons be seized yet running fairly well on 2 cylinders and have 140 compression on the 3rd? The paint was not scorched on the head but it did get hot enough to melt the poppett valves. Once it overheated to the point it stalled, I never attempted to start it again until I replaced the impeller. When I had the head off, nothing was glaring at me as far as bad pistons, but then again I have limited experience. I did replace the exhaust manifold baffle plate along with the manifold and related gaskets.

 

[F_R]

Whatever.

 

[ct1762@gmail.com]

sounds like the #3 cylinder has shot skirts... cannot pull enough fuel/air mix in. i've done 1/2 dozen of these this year, including the 2 cyl looper versions and after a bore/hone job, they idle perfectly with plenty of power. you'd be amazed what a complete rebuild can do... shows you how these really ran when brand new. all little issues of a tired motor vanish!

 

[F_R]

sounds like the #3 cylinder has shot skirts... cannot pull enough fuel/air mix in. i've done 1/2 dozen of these this year, including the 2 cyl looper versions and after a bore/hone job, they idle perfectly with plenty of power. you'd be amazed what a complete rebuild can do... shows you how these really ran when brand new. all little issues of a tired motor vanish!

Guess what isolates the exhaust ports from the crankcase.

 

[Capt dave 258]

I am not sure what shot skirts is but is there a way I can test to insure that is the issue? Thanks for your input and have patience as I am learning as I go along.

 

[F_R]

He is talking about scored piston skirts. A compression test can evaluate the condition of the piston rings, but not the piston skirts. Unlike a four-stroke, a two-stroke crankcase must also hold compression and vacuum to pump fuel/air into the cylinders. The piston skirts are important in this respect. The cylinder's exhaust ports would have a direct connection to the crankcase if it were not for the fit of the piston skirt to cylinder.

You could have gotten a partial view when you had the exhaust cover off. Anything more requires an engine tear-down.

 

[RBoyd1971]

I'm not sure I'm buying all that y'all are selling. I mean no disrespect, however I've got an 82 model 90 hp with 140 psi on cylinder number 3. If you look through the intake cover, you can see a pretty scored piston skirt. Likely from that one cylinder overheating or some dummy cranking on starting fluid at one time. Luckily it wasn't all the way up to the rings where it would cause sticking. However, it idles like a dream and runs well. Just how bad would they have to be? I removed the head on that side and removed the aluminium that was galded to the cylinder wall near the intake port and brought the compression up from 130 to 140. There was a very small patch on the exhaust side as well. Now granted, all the other pistons are in excellent shape.

 

[Capt dave 258]

Thank you all for your input. Not quite sure what I'm going to do next

 

[oldboat1]

All pretty complicated, unless it ain't. Possible the middle carb float valve is not opening to allow in fuel. If there was a rebuild kit requiring the small wire hook to lift the needle (which has a sometimes sticky tip), Still could be a basket case, but maybe a better running basket case.

 

[Capt dave 258]

I'm going to see if I can switch out the bottom carb with the top or middle carb and see if the problem stays the same or moves to the cylinder that gets the bottom carb. That should tell me if the problem is in the carb or within the motor itself.